Our invention is in the general area of orthopedic prostheses, particularly, artificial knees. Specifically, our invention is a tibial prosthesis for an artificial knee. The tibial prosthesis comprises a base plate affixed to an upper, resected surface of a tibia and an articulating surface which pivots about an axis within the medial condylar compartment.
The two largest and longest bones of the human body, the femur and tibia, meet at a person's knee. The tibia is situated at the front and inner side of the lower leg. It is prismoid in form, and expanded above where it enters into the knee joint. The head of the tibia is large and expanded on each side into two eminences, the tuberosities. These eminences form two smooth concave compartments or surfaces which articulate with the condyles of the femur. The medial condyle is more prominent anteriorly and broader both in the anteriorposterior and transverse diameters than the lateral condyle. Accordingly, the lateral articular surface of the tibia is longer, deeper and narrower than the medial surface of the tibia. The medial surface is broader, more circular, and concave from side to side. The anterior surfaces of the tuberosities are continuous with one another, forming a single large surface which is somewhat flattened. Posteriorly the tuberosities are separated from each other by a shallow depression for attachement of ligaments. The medial tuberosity presents posteriorly a deep transverse groove for the insertion of a tendon.
Because of aging or disease, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to surgically remove either the condyles or the tuberosities or both and replace these structures with prosthetic implants.
Tibial prostheses commonly comprise titanium base plates with polyethylene articulating surfaces mounted thereon. To accommodate the range of motion of the human knee, either the femoral condyles or a femoral prosthesis rocks against the articulating surface of the tibial prosthesis. This rocking action can wear away the articulating surface.
Bone cell death (osteolysis) has been linked to polyethylene wear debris. Long-term loosening of implant systems may be caused by osteolysis due to polyethylene debris. Although it is not known if a physiological threshold for wear debris exists, a decrease in the amount wear particles is a positive achievement.